LANSING, MI - Republican presidential candidate Mitt Romney could name his running mate at any moment.

And depending on the day, a new "front-runner" emerges to become the favorite - especially when Romney campaigns with anyone on his closely held but widely speculated about short list.

Here's what we know:

- He will name his vice presidential candidate before the Republican National Covention that starts in late August. According to the Associated Press, an announcement could come this week.

- Though there's always the chance for a surprise pick - Sarah Palin anyone? - Romney most likely will go with a known quantity.

Who? MLive has compiled a list of seven of the most-mentioned candidates, with links to articles and blogs laying out the positives and negatives of each.

Tim Pawlenty

- U.S. Sen. Rob Portman of Ohio, 56. Pros: He has the experience, he's from a must-have swing state for Romney and he is trusted. Cons: He could be seen as a "boring" choice, and tea party groups don't like that he was President George W. Bush's budget director when the deficit doubled (during the worst recession since the Great Depression.)

- Former Minnesota Gov. Tim Pawlenty, 51. Pros: His working-class upbringing, Christian faith and his eight years as governor of a Democratic-leaning state make him appealing. Pawlenty was considered by John McCain in 2008 before he went with Palin. Cons: He is seen as too safe of a pick and not someone who can excite people about the GOP ticket.

Bobby Jindal

- Louisiana Gov. Bobby Jindal, 41. Pros: Some social conservatives have not been sold on Romney, and Jindal would help in that department. He's young, seen as a wunderkind and policy wonk, and he's in a unique position to debate energy policy given the BP oil spill. He frequently criticizes President Barack Obama for ordering a moratorium on Gulf drilling. Cons: His response to Obama's first State of the Union address in 2009 was panned, leaving some uncertainty about how he'd do in a national campaign.

Marco Rubio

- U.S. Sen. Marco Rubio of Florida, 41. Pros: Also young, Rubio is Latino and from a crucial battleground state. He's seen as a rising star by Republicans, a favorite of Christians and tea party enthusiasts. Cons: He's relatively inexperienced on the national stage (though Obama was, too), and he's had to defend against questions over whether he embellished details of his parents' emigration from Cuba.

- U.S. Sen. Kelly Ayotte of New Hampshire, 42. Pros: She could help Romney make inroads with female voters, and has a law-and-order background as former attorney general of the state. Cons: As with Palin, people would wonder who she is, and it would not help Romney - a former governor of Massachusetts - have a diverse ticket geographically.